Fabrication of focus grill type cathode ray tubes

ABSTRACT

Prior to assembly of the envelope of a focus grill tube, the cup-shaped panel portion of the envelope is wound with a wire helix which is disposed around and along the panel, each turn of the helix extending across the open side of the panel in predisposed relation with a pattern of phosphor strips on the bottom wall of the panel. Preferably, the helix turns are disposed in grooves in the end surface of the side wall of the panel, and portions of each helix turn are disposed about a member having a thermal expansion greater than that of the helix wire.

United States Patent [1 1 Law [451 Mar. 27, 1973 FABRICATION OF FOCUS GRILL TYPE CATHODE RAY TUBES [75] Inventor: Harold Bell Law, Princeton, NJ.

[73] Assignee: Y RCA Corporation, New York, NY.

[22] Filed: Nov. 10, 1971 21 Appl. No.: 197,267

[52] US. Cl. ..29/25.16, 29/25.13, 140/7l.5 [51] Int. Cl ..H0lj 9/18 [58] Field of Search ..29/25.l, 25.ll,25.l3,25.l5,

3,600,778 8/1971 Martin 140/7 1 .6 X

Primary Examiner-J. Spencer Overholser Assistant Examiner-Richard Bernard Larazus Att0mey-G. H. Bruestle ABSTRACT Prior to assembly of the envelope of a focus grill tube, the cup-shaped panel portion of the envelope is wound with a wire helix which is disposed around and along the panel, each turn of the helix extending across the open side of the panel in predisposed relation with a pattern of phosphor strips on the bottom wall of the panel. Preferably, the helix turns are disposed in grooves in the end surface of the side wall of the panel, and portions of each helix turn are disposed about a member having a thermal expansion greater than that of the helix wire.

5 Claims, 5

FABRICATION OF FOCUS GRILL TYPE CATHODE RAY TUBES BACKGROUND OF THE INVENTION This invention relates to the fabrication of cathode ray tubes, and particularly to the fabrication of color television picture tubes of the focus grill" type.

One type of focus grill color picture tube comprises a glass envelope including a cup-shaped panel having a phosphor screen on the inside surface thereof, and a funnel-shaped envelope with thelarge end thereof sealed to the open end of the panel in co-axial relation therewith. For the purpose of properly focusing or directing an electron beam or beams onto I desired portions of the screen, a grill comprising one or more sets of parallel fine wires is disposed within the tube closely adjacent to the panel screen.

In the fabrication of such tubes, according to one prior art technique, a plurality of grooves are provided in the end surface of the side wall of the cup-shaped panel, and the phosphor screen is printed on the inside of the panel in preselected relation with the grooves. A separate grill assembly is prepared comprising an annular frame of a size larger than that of the panel, and a plurality of fine wires stretched across the frame opening and bonded to the frame sides. The grill assembly is disposed around the panel over the open side thereof with the fine wires disposed within the grooves and extending across the panel opening. The frame is pulled downwardly of, the panel to maintain the wires under tension across thepanel opening, and the funnel member is frit-sealed to the end surface of the panel side wall, the frit joint closing the grooves and anchoring the wires therein. The grill assembly frame and the wire portions extending outwardly from the tube are then removed.

One problem with this prior art fabrication technique is that the panel grooves are preferably shallow, to provide a reliable, hermetic seal with the funnel, and during movement of the tube assembly prior to and during the sealing operation, e.g., movement of the tube assembly on a conveyor through a sealing furnace, the fine grill wires are subject to being displaced from the grooves. This adversely affects the alignment of the grill wires with the phosphor pattern on the screen and results in defective picture tubes.

DESCRIPTION OF THE DRAWING FIG. 1 is a side view, partly broken away, of a cathode ray tube of a type in which the instant'invention has utility;

FIG. 2 is a cross-sectional view, partly broken away, taken along line 2-2 of FIG. 1;

FIG. 3 is a plan view of a panel member of a type used in the practice of the method of this invention;

FIG. 4 is a side view, partly broken away, and partly schematic, showing apparatus for winding a wire around and along the panel member shown in FIG. 3; and

FIG. 5 is a plan view of the apparatusshown in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Focus grill cathode ray tubes, with which the invention has particular utility, are known" see, for example, US. Pat. No. 3,030,536, issued Apr. 17, 1962, and No. 2,842,696, issued July 8, 1958.

In general, as shown in FIG. 1 herein, such tubes comprise a glass envelope 10 including a cup-shaped panel member 12, -a frusto-conical shaped funnel member 14, and a cylindrical neck tubulation member 16. The panel and funnel members are frit-sealed together in co-axial relation, e.g., the contacting edges of the separate members are coated with a glass frit, the

5 contacting edges are abutted against one another and heated to liquify the glass frit, and the liquid glass, upon further heating, solidifies to bond the edges together. The funnel 14 and the neck 16 are sealed by softening and fusing the abutting glass edges thereof.

The inside surface 18 of the bottom wall or faceplate 20 of the panel 12 is provided with a plurality of parallel contiguous strips 22 of phosphor arranged in sets of three adjacent strips 22, the strips of each set being of different phosphors to provide different colors when the strips are energized by an electron beam. The phosphor coated panel surface 18 is the screen" of the tube. The screen 18 hasa generally rectangular shape, having a major axis 24 (FIG. 2) and a minor axis 26.

Disposed within the tube in spaced, close relation with the screen 18 is a grill. 30 comprising a plurality of fine wires 32 which extend parallel to the phosphor strips 22.

The funnel member 14 may include various focusing and accelerating electrodes, and the neck member 16 may include one or more electron guns. Details of these latter members are known and form no part of the instant invention. Also, the operation of tubes of this type is generally known.

In the fabrication of a tube of the type shown in FIG. 1, in accordance with this invention, a panel 12 is first provided as a separate member including, as. shown in 'FIG. 3, a pattern of contiguous phosphor strips 22 on the faceplate 18 thereof, and a plurality of grooves 42 in the end surface 44 of the side wall 46 of the panel. The grooves 42 are disposed in two arrays 50 and 52 of grooves on oppositely disposed portions of the side wall 46, each groove 42 in one array 50 having a corresponding oppositely disposed groove 42 in the other array 52.

The phosphor strips 22 can be provided on the screen by known printing methods using a photosensitive binder, and the arrays 50 and 52 of grooves'can be provided by known means such as etching.

Of importance, is that the arrays 50 and 52 of grooves are located in accurate relation with respect to the strips 22. Such accurate location can be provided, for example, by the use of indicia means on the panel 12 to which both the grooves 42 and the strips 22 can be referenced. For example, the panel 12, in this embodiment, is provided with three positioning lugs 54 which are integral therewith. After the panel is formed, as by molding, according to known processes, the lugs 54 are accurately machined, as by grinding,,to provide indicia means which are the same from panel to panel. A further function of the lugs 54 is described hereinafter.

Having provided the panel 12, the grill 30 therefor is next provided by winding a helix of a fine wire 32 around and along the panel. To this end, a winding cradle 60 (FIGS. 4 and 5) comprising a cup-shaped member is provided for receipt of the panel 12 therein with the side wall 46 of the panel extending at least slightly beyond the side wall 62 of the cradle, as shown.

The cradle 60 is provided with three positioning screws 63, 64, and 65 which extend through the cradle side wall 62, and two leaf springs 66 and 67 mounted on the inside of the side wall 62. When a panel 12 is disposed within the cradle 60, the screw 63, in combination with the spring 66, is used to position the panel 12 along the major axis 68 of the cradle, and the screws 64 and 65, in combination with the spring 67, are used to position the panel 12 in the direction perpendicular to the cradle axis .68 as well as to angularly orient the panel 12 within the cradle 60. The purpose of angularly orienting the panel'l2 relative to the cradle 60 is described below. The screws 63, 64, and 65, in combination with the springs 66 and 67 serve to lock the panel 12 within the cradle 60. Additionally, clamps 71 can be provided to further lock the panel 12 in place.

The cradle 60 is also provided with two co-axial pointed cylindrical pins 69 by means of which the eradle 60 can be rotated about the major axis 68 of the cradle.

To wind a wire helix about the panel 12, the cradle 60, with the panel 12 located therein, is mounted between centers of a conventional lathe-like winding apparatus (not shown), the cradle 60 is rotated about its axis 68, and a wire 32 from a spool 70 (FIG. 4) is attached to the cradle 60 by a suitable clamp 74 and is thus drawn onto and around the panel and cradle. Known, means, not shown, are provided for advancing the spool 70 in a direction parallel to the axis of rotation of the cradle.

As shown in FIG. 5, the axis 68 of rotation of the cradle 60 is slightly off-set from the major axis 24 of the panel 12. The purpose of the off-set is to off-set the grooves 42 of each groove array 50 and 52 from each other an amount equal to the amount of advance of the spool 70 during the cradle rotation in order that each turn of the helix wound about the cradle-panel assembly is disposed within a pair of corresponding grooves 42 of each groove assembly. Selection of the off-set of the cradle axis 68 relative to the panel major axis 24, the rate of rotation of the cradle 60, and the rate of advance of the spool 70 in order to properly lay the wire 32 in successive pairs of corresponding grooves 42 of the groove arrays 50 and 52 is well within the skill of persons familiar with the helix winding art. Aside from providing the off-set of the panel and cradle axis, as described, the positioning screws 63, 64, and 65 allow adjustment of the position of the panel 12 relative to the winding apparatus.

As shown in FIGS. 4 and 5, as a result of the winding operation, a helix of wire 32 is wound about the cradlepanel assembly. The end turn of the helix is also secured to the cradle by a suitable clamp, not shown. A reason for winding the wire 32 around the cradle 60, as well as around the panel 12, is described hereinafter.

The wire 32 is preferably wound at a relatively. high tension for maintaining the wire turns firmly in place around the cradle 60 and within the grooves 42 of the panel 12. Thus, during subsequent processing of the cradle-panel assembly, e.g., the sealing of the funnel 14 to the panel 12, little danger exists that the wire 32 will be displaced from the grooves 42.

In one embodiment of the invention, the wire 32 comprises 2 mil diameter stainless steel, and the wire is wound at 40 turns to the inch under a tension of 6 ounces. The grooves 42 have a circular cross-section, and have a width of 3 mils and a depth of 2.mils.

The wound panel 12 is now assembled into a cathode ray-tube using known techniques. Thus, for example, a layer of glass frit is disposed along the end surface 44 of the panel side wall 46 and along the mating edge of the funnel member 14, the funnel 14' and panel 12 are pressed into an abutting, co-axial relationship, and the abutting edges of the members are heated to soften the glass frit to provide a frit seal of the contacting edges. In the sealing process, the funnel 14 can be disposed on a suitable carrier of a conveyor system, with the large open side of the funnel facing upwardly, the cradlepanel sub-assembly is disposed within the carrier with the open end of the panel 12 facing downwardly and disposed in contact with the open end of the funnel 14,

and the loaded carrier is conveyed through an oven to perform the sealing process. The use of such conveyors and oven is known in the cathode ray tube arts.

During the funnel-to-panel sealing process, the glass frit flows into the grooves 42 thereby sealing the grooves and sealing the wires32 therein. Preferably, in

order that the wires 32 are firmly anchored to the panel, a wire 32 is used which is wet by the glass frit. The use of glass frit for sealing together envelope portions of cathode ray tubes and for making adherent, hermetic seals to metal members is generally known.

Then, the portions of the wires 32 disposed on the outside of the tube envelope are removed, as by cuttingwith a razor edge, to complete the inventive process. The tube 10 can then be separated from the cradle. If desired, electrical contact to the various wires 32, for

' the purpose of applying an electric potential thereto,

can be made by disposing a conductive paint on the tube envelope 10 around the joint between the panel 12 and the funnel 14. Since the wires 32 extend at least a small distance outwardly of the envelope after the 1 cutting operation, the wires are contacted by the conthe wire 32, the cradle expands more than the wire turns, thus maintaining the tension of the helix turns .and minimizing the danger of the turns becoming displaced from the panel grooves during the panel-to-funnel sealing operation.

While the use of a cradle of the type shown provides a simple means for both mounting the panel 12 for rotation and maintaining the helix turns under tension during heating thereof, the use of the particular cradle 60 described herein is not essential. For exam-- ple, other fixture means employing suitable jaws or the like can be used for mounting the panel 12 for rotation.

Also, other expansion means can be used to maintain the helix turns under tension during the envelope sealing process. For example, a separate plate of aluminum or the like can be disposed along the outside of the bottom wall of the panel between the helix turns and the panel. Or, in place of a thermal expansion member, such as the aluminum plate, a compressive expansion member, such as a hollow cylinder, can be used; the

member being compressed as the helix is wound sealing portions of said helix turns to the side wall of I maintaining the turns of said helix under tension during heating ofsaid helix.

4. A method of fabricating an electron discharge tube comprising a generally cup-shaped panel having a bottom wall and a side wall, and an open-ended envelope member, the open end of said envelope member being sealed to the end surface of the side wall of said panel, said method comprising: I

providing a patterned layer of phosphor on the bottom wall of said panel;

providing an array of grooves in each of a pair of oppositely disposed portions of the end surface of said side wall, each groove of one array having a corresponding oppositely disposed groove in the other of said arrays, and said arrays of grooves being in predetermined position with respect to said phosphor pattern;

winding a wire helix around said panel, each turn of said helixextending across the open end of said panel within and between two corresponding grooves of each of said groove arrays;

frit-sealing the end of said envelope member to sad end surface of said panel, thereby sealing said turns within said grooves; and

removing the portions of said turns extending around the outside of said panel.

5. The method of claim 4 wherein said winding step includes disposing a member having a thermal expansion greater than that of said wire between said helix and said panel for maintaining the turns of said helix under tension during said sealing operation. 

1. A method of fabricating an electron discharge tube comprising a generally cup-shaped panel, said method comprising: winding a helix of wire around the outside of and along said panel, the turns of said helix extending across the open end of said panel in preselected relation with respect to a pattern of phosphor on the bottom wall of said panel; sealing portions of said helix turns to the side wall of said panel; and removing the portions of said helix extending around the outside of said panel.
 2. The method of claim 1 wherein said winding step comprises disposing each helix turn in a pair of oppositely disposed grooves in the end surface of said side wall.
 3. The method of claim 1 including disposing an expansion member between said helix and said panel for maintaining the turns of said helix under tension during heating of said helix.
 4. A method of fabricating an electron discharge tube comprising a generally cup-shaped panel having a bottom wall and a side wall, and an open-ended envelope member, the open end of said envelope member being sealed to the end surface of the side wall of saId panel, said method comprising: providing a patterned layer of phosphor on the bottom wall of said panel; providing an array of grooves in each of a pair of oppositely disposed portions of the end surface of said side wall, each groove of one array having a corresponding oppositely disposed groove in the other of said arrays, and said arrays of grooves being in predetermined position with respect to said phosphor pattern; winding a wire helix around said panel, each turn of said helix extending across the open end of said panel within and between two corresponding grooves of each of said groove arrays; frit-sealing the end of said envelope member to sad end surface of said panel, thereby sealing said turns within said grooves; and removing the portions of said turns extending around the outside of said panel.
 5. The method of claim 4 wherein said winding step includes disposing a member having a thermal expansion greater than that of said wire between said helix and said panel for maintaining the turns of said helix under tension during said sealing operation. 